The present disclosure relates to a terahertz band filter, and more particularly, to a terahertz notch filter for blocking a terahertz wave in a specific band, and a terahertz low pass filter for passing a terahertz wave in a low frequency band.
Terahertz waves are electromagnetic waves in a near infrared region between microwaves and light waves. Such a terahertz wave has a frequency ranging from approximately 0.1 THz to approximately 10 THz, a wavelength ranging from approximately 0.03 mm to approximately 3 mm, and an energy ranging from approximately 0.4 meV to approximately 40 meV. Since the production and detection of terahertz waves as electromagnetic waves were technically limited, they were unexplored. However, as a femtosecond laser is developed as a light source for terahertz waves, the production and detection of terahertz waves are possible, and active research on terahertz bands is recently carried out on a global scale.
Since terahertz bands are between a microwave band and a light wave band, terahertz waves have both the rectilinear propagation of light and the transmissivity of electromagnetic waves, and easily pass through a material that blocks a microwave or light wave. In addition, terahertz waves are easily absorbed into moisture. Accordingly, terahertz waves are applied to various fields such as medicine, medical engineering, biochemistry, food technology, pollution watching, and security inspection, and their importance increases. Furthermore, terahertz waves are applied to various types of application technology such as nanotechnology, information technology, bio technology, environmental technology, space technology, and military technology. To this end, the development of passive devices such as terahertz waveguides, filters, and resonators is required.
Especially, the development of terahertz waveguides is required for local transmission between boards of integrated circuits, and transmission between devices. Recently, tapered parallel plate waveguides (TPPWGs), circular metal waveguides, rectangular metal waveguides, single crystal sapphire fibers, transmission lines, single metal wires, coaxial cables, and parallel-plate waveguides are introduced, which are passive devices adapted for a single mode propagation in a terahertz region.
FIG. 1 is a perspective view illustrating tapered parallel plate waveguides in the related art.
Referring to FIG. 1, tapered parallel plate waveguides include a pair of metal plates 11 and 12 which are opposed to each other to form parallel surfaces 11a and 12a along which a terahertz wave propagates. An input end 10a and an output end 10b are integrated into the metal plates 11 and 12 forming the parallel surfaces 11a and 12a. The input end 10a and the output end 10b include pairs of slopes 11b and 12b that gradually decrease in distance therebetween until reaching a distance between the parallel surfaces 11a and 12a. That is, each of the metal plates 11 and 12 includes the parallel surface 11a or 12a and the slopes 11b or 12b disposed at ends thereof and inclined from the parallel surface 11a or 12a, and the metal plates 11 and 12 are coupled to each other to face each other with a space therebetween, to thereby form tapered parallel plate waveguides 1 to which the input end 10a and the output end 10b are integrated. Accordingly, inclination angles of the tapered parallel plate waveguides 1 including the slopes 11b and 12b at the ends thereof improve coupling efficiency, and make it possible to propagate terahertz waveforms in a practical transverse electro magnetic (TEM) mode.
Although practical TEM mode propagation through tapered parallel plate waveguides (TPPWGs) is realized, a resonant cavity on a surface of an optical waveguide, a photonic crystal, and the like are continually researched. Especially, filtering (notch filtering or low pass filtering) within a specific band is needed in terahertz wave propagation. Since filters for filtering within a specific band in terahertz wave propagation as described above (hereinafter, referred to as terahertz band filters) are variously applied to terahertz communications, and the research and development of sensors and devices, their development is urgently needed.